In reply to Bonnie.
I find aphids often attack young or stressed plants. My tomatoes were a bit stressed for water in my glasshouse recently and were getting attacked. My first line of defence is to support the leaves with my hand and squirt the aphids off with a hose. Then I give the plant a good feed of worm wee or comfrey tea and a good soak with water and that often sorts them out. Squashing aphids is also quite satisfying. If that isn't doing the trick you can brew up a soapy water, garlic or rhubarb leaf spray for them. Exact recipes could be found in any good organic book, I'd just chuck half a dozen garlic cloves in boiling water, chop up a rhubarb leaf, cool and then add a dash of soap, sieve, dilute and spray. Probably diluting by 1:10 but to be honest I usually trust my sense of smell and stop adding water when it doesn't smell too toxic. Or use natural pyrethrum spray which you can make or buy, beware though it can kill the good bugs too. I have to confess I haven't bothered with these methods for a couple of years as the water and feed method usually works for me. Also establishing a good balance of other insects in the garden will help keep aphids in balance. Lady bugs and praying mantis LOVE aphids to eat. I catch them off my poor neglected roses and place them on the precious vege plants. I grow cleome, mustard and flowering herbs to attract the good guys into the garden. Also they love things like parsley, rocket, carrot and parsnip left to go to seed. Good luck hope you can find something here that works, perhaps others can add comments if they have any other suggestions.